Colorless precursor of alkyl viologen as filter agent in photographic film

ABSTRACT

The present invention is directed to a photographic film unit adapted to provide, by diffusion transfer processing, selective dye image recordation of incident actinic radiation as a function of the point-to-point degree of photosensitive element exposure, which film unit includes a plurality of layers including a photosensitive silver halide layer having associated therewith dye image-forming material which is diffusible as a function of the point-to-point degree of silver halide layer exposure to actinic radiation; and associated with at least one of said silver halide layers an initially substantially colorless precursor of an alkyl viologen dye, i.e., a photographically inactive compound, adapted to provide an alkyl viologen in an amount effective to prevent photoexposure of the silver halide layer when the film unit is removed from the camera for processing by the filtering and/or silver halide desensitization action of the dye.

United States Patent Greenwald Nov. 13, 1973 COLORLESS PRECURSOR OF ALKYL Primary Examiner-Norman G. Torchin VIOLOGEN AS FILTER AGENT IN PHOTOGRAPHIC FILM Inventor: Richard B. Greenwald,

Framingham, Mass.

Assignee: Polaroid Corporation, Cambridge,

Mass.

Filed: June 9, 1972 Appl. No.: 261,261

Assistant Examiner-Richard L. Schilling Att0meyRobert M. Ford et al.

[5 7] ABSTRACT The present invention is directed to a photographic film unit adapted to provide, by diffusion transfer processing, selective dye image recordation of incident actinic radiation as a function of the point-to-point degree of photosensitive element exposure, which film unit includes a plurality of layers including a photosensitive silver halide layer having associated therewith dye image-forming material which is diffusible as a function of the point-to-point degree of silver halide layer exposure to actinic radiation; and associated with at least one of said silver halide layers an initially substantially colorless precursor of an alkyl viologen dye, i.e., a photographically inactive compound, adapted to provide an alkyl viologen in an amount effective to prevent photoexposure of the silver halide layer when the film unit is removed from the camera for processing by the filtering and/or silver halide desensitization action of the dye.

22 Claims, 7 Drawing Figures PATENTED NOV 1 3 I975 SHEET 10F 4 PATEN IEUNuv 13 ms BLT/2.02s

SHEET 2 BF 4 SHEET u 0F 4 PATENTED HOV 13 I973 COLORLESS PRECURSOR OF ALKYL VIOLOGEN AS FILTER AGENT IN PI'IOTOGRAPHIC FILM BACKGROUND OF THE INVENTION This invention is concerned with photography and, more particularly, with photographic processes which are conducted outside of a camera and wherein undesired post-imaging fog is prevented by a light-absorbing reagent retained within the ultimate photograph, and with photographic products useful in performing such processes.

A number of photographic processes by which images may be developed and viewed within seconds or minutes after exposure have been proposed. Such processes generally employ a processing composition which is suitably distributed between two sheet-like elements, the desired image being carried by one of said sheetlike elements. The resulting iamges may be in blackand-white, e.g., in silver, or in one or more colors. Processing may be conducted in or outside of a camera. The most useful of such processes are the diffusion transfer processes which have been proposed for forming silver or dye images, and several of these processes have been commercialized. Such processes have in common the feature that the final image is a function of the formation of an image-wise distribution of an image-providing reagent and the diffusion transfer of said distribution to or from the stratum carrying the final image, whether positive or negative. It has also been proposed to form the final desired image in the photosensitive stratum per se by monobath processing to obtain a negative image or by so-called direct positive processing to obtain a positive image, employing processing techniques and physical film structures similar to those found useful in diffusion transfer processing. This invention is directed to providing techniques and film structures by which photographic processes, such as those noted above, may be performed, at least in part, outside of a camera.

As indicated above, this invention is primarily directed to photographic processes wherein the desired image is obtained by processing an exposed photosensitive material, preferably silver halide, with a processing composition distributed between two sheet-like elements, one of said elements including said photosensitive material. The processing composition is so applied and confined within and between the two sheet-like elements as not to contact or wet outer surfaces of the superposed elements, thus providing a film unit or film packet whose external surfaces are dry. The processing composition may be viscous or nonviscous, and preferably is distributed from a single-use rupturable container; such pressure rupturable processing containers are frequently referred to as pods. The final image may be black-and-white, monochrome or multicolor and either negative or positive with respect to the photographed subject. The present invention is especially, if not uniquely, adapted for facilitating processing outside of a camera film units which are maintained as an integral laminate after processing, the desired image being viewed through one face of said laminate.

In diffusion transfer system embodiments of the present invention, such systems rely for color image formation upon a differential in mobility or solubility of a dye image-providing material obtained as a function of development so as to provide an imagewise distribution of such material which is more diffusible and which is therefore selectively transferred, at least in part, by diffusion, to a superposed dyeable stratum to impart thereto the desired color transfer image. The differential in mobility or solubility may for example be obtained by a chemical action such as a redox reaction or a coupling reaction.

The dye image-providing materials which may be employed in such processes generally may be characterized as either (I) initially soluble or diffusible in the processing composition but are selectively rendered non-diffusible in an imagewise pattern as a function of development; or (2) initially insoluble or non-diffusible in the processing composition but which are selectively rendered diffusible in an imagewise pattern as a function of development. These materials may be complete dyes or dye intermediates, e.g., color couplers.

As examples of initially soluble or diffusible materials and their application in color diffusion transfer, mention may be made of those disclosed, for example, in U. S. Pat. Nos. 2,647,049; 2,661,293; 2,698,244; 2,698,798; 2,802,735; 2,774,668; and 2,983,606. As examples of initially non-diffusible materials and their use in color transfer systems, mention may be made of the materials and systems disclosed in U. S. Pat. Nos. 3,443,939; 3,443,940; 3,227,550; 3,227,551; 3,227,552; 3,227,554; 3,243,294 and 3,445,228.

In any of these systems, multicolor images are obtained by employing a film unit containing at least two selectively sensitized silver halide layers each having associated therewith a dye image-providing material exhibiting desired spectral absorption characteristics. The most commonly employed elements of this type are the so-called tripack structures employing a blue-, a greenand a red-sensitive silver halide layer having associated therewith, respectively, a yellow, a magenta and a cyan dye image-providing material.

A particularly useful system for forming color images by diffusion transfer is that described in U. S. Pat. No. 2,983,606, employing dye developers (dyes which are also silver halide developing agents) as the dye imageproviding materials. In such systems, a photosensitive element comprising at least one silver halide layer having a dye developer associated therewith (in the same or in an adjacent layer) is developed by applying an aqueous alkaline processing composition. Exposed and developable silver halide is developed by the dye developer which in turn beocmes oxidized to provide an oxidation product which is appreciably less diffusible than the unreacted dye developer, thereby providing an imagewise distribution of diffusible dye developer in terms of unexposed areas of the silver halide layer, which imagewise distribution is then transferred, at least in part, by diffusion, to a dyeable stratum to impart thereto a positive dye transfer image. Multicolor images may be obtained with a photosensitive element having two or more selectively sensitized silver halide layers and associated dye developers, a tripack structure of the type described above and in various patents including the aforementioned U. S. Pat. No. 2,983,606 being especially suitable for accurate color recordation of the original subject matter.

In color diffusion transfer systems of the foregoing description, color images are obtained by exposing a photosensitive element or negative component comprising at least a light-sensitive layer, e.g., a gelatino silver halide emulsion layer, having a dye imageproviding material associated therewith in the same or in an adjacent layer, to form a developable image; developing this exposed element with a processing composition to form an imagewise distribution of a soluble and diffusible image-providing material; and transferring this imagewise distribution, at least in part, by dif fusion, to a superposed receiving element or positive component" comprising at least a dyeable stratum to impart to this stratum a color transfer image. The negative and positive components may be separate elements which are brought together during processing and thereafter either retained together as the final print or separated following image formation; or they may together comprise a unitary structure, e.g., integral negative-positive film units wherein the negative and positive components are laminated and/or otherwise physically retained together at least prior to image formation.

While the present invention is applicable both to those systems wherein the dyeable stratum is contained on a separate element and to those systems wherein the dyeable stratum and the photosensitive strata comprise a unitary structure, of particular interest are those integral negative-positive filrn units adapted for forming color transfer images viewable without separation, i.e., wherein the positive component need not be separated from the negative component for viewing purposes. Generally, such film units comprise a plurality of essential layers including a negative component comprising at least one light-sensitive silver halide and associated dye image-providing material and a positive component comprising dyeable stratum. These components may be laminated together or otherwise secured together in physical juxtaposition as a single structure. Film units intended to provide multicolor images comprise two or more selectively sensitized silver halide layers each having associated therewith an appropriate dye image-providing material exhibiting desired spectral absorption characteristics. As was heretofore mentioned the most commonly employed negative components for forming multicolor images are of the tripack structure containing a blue, a greenand a redsensitive silver halide layer having associated therewith in the same or in a contiguous layer a yellow, a magenta and a cyan dye image-providing material respectively. lnterlayers or spacer layers may if desired be provided between the respective silver halide layers and associated dye image-providing materials. in addition to the aforementioned essential layers, such film units further include means for providing a reflecting layer between the dyeable stratum and the negative component in order to mask effectively the silver image of images formed as a function of development of the silver halide layer or layers and any remaining associated dye image-providing material and to provide a background for viewing the color image formed in the dyeable stratum, without separation, by reflected light. This reflecting layer may comprise a preformed layer of a reflecting agent included in the essential layers of the film unit or the reflecting agent may be provided after photoexposure, eg., by including the reflecting agent in the processing composition. These essential layers are pref erably contained on a transparent dimensionally stable layer or support member positioned closest to the dyeable stratum so that the resulting transfer image is viewable through this transparent layer. Most preferably another dimensionally stable layer which may be transparent or opaque is positioned on the opposed surface of the essential layers so that the aforementioned essential layers are sandwiched or confined between a pair of dimensionally stable layers or support members, at least one of which is transparent to permit viewing therethrough of a color transfer image obtained as a function of development of the exposed film unit in accordance with the known color diffusion transfer system such as will be detailed hereinafter. In a particularly preferred form such film units are employed in conjunction with a rupturable container of known description containing the requisite processing composition and adapted upon application of pressure of applying its contents to develop the exposed film unit, e.g., by applying the processing composition in a substantially uniform layer between the dyeable stratum and the negative component. It will be appreciated that the film unit may optionally contain other layers performing specific desired functions, e.g., spacer layers, etc.

in general, the integral negative-positive film units of the foregoing description, e.g., those described in the aforementioned patents, are exposed to form a developable image and thereafter developed by applying the appropriate processing composition to develop exposed silver halide and to form, as a function of development, an imagewise distribution of diffusible dye image-providing material which is transferred, at least in part by diffusion, to the dyeable stratum to impart thereto the desired color transfer image, e.g., a positive color transfer image. Common to all of these systems is the provision of a reflecting layer between the dyeable stratum and the photosensitive strata to mask effectively the latter and to provide a background for viewing the color image contained in the dyeable stratum, whereby this image is viewable without separation, from the other layers or elements of the film unit. in certain of these systems, this reflecting layer is provided prior to photoexposure, e.g., as a preformed layer included in the essential layers of the laminar structure comprising the film unit, and in others it is provided at some time thereafter, e.g., by including a suitable lightreflccting agent, for example, a white pigment such as titanium dioxide, in the processing composition which is applied between the dyeable stratum and the next adjacent layer to develop the latent image and to form the color transfer image.

The dye image-providing materials which may be employed in such processes generally are selected from those materials heretofore mentioned and disclosed in the illustrative patents which were initially soluble or diffusible in the processing composition but which are selectively rendered non-diffusible as a function of development or those which are initially insoluble or nondiffusible in the processing composition but are selectively rendered diffusible as a function of development. These materials may be complete dyes or dye intermediates, e.g., color couplers.

U. S. Pat. No. 3,415,644, 3,415,645 and 3,415,656, all issued Dec. 10, 1968 in the name of Edwin H. Land, disclose and claim photographic products and processes wherein a photosensitive element and an imagereceiving element are maintained in fixed relationship prior to exposure, and this relationship is maintained as a laminate after processing and image formation, in these processes, the final image is viewed through a transparent (support) element against a reflecting, i.e., white background. ln a particularly useful embodimerit, photoexposure is made through said transparent element and application of the processing composition provides a layer of light-reflecting material to provide a white background. The light-reflecting material (referred to in said patents and applications as an opacifying agent) is preferably titanium dioxide, and it also performs an opacifying function, i.e., it is effective to mask the developed silver halide emulsions so that the transfer image may be viewed without interference therefrom, and it also helps to protect the photoexposed silver halide emulsions from post-exposure fogging by light passing through said transparent layer if the photoexposed film unit is removed from the camera before image-formation is completed. The present invention is directed to improvements in the processes and products disclosed in the said patents and is particularly directed to providing light-absorbing materials effective to permit performing said processes outside of the camera in which photoexposure is effected. For convenience, the specifications of the said patents and applications are hereby specifically incorporated herein.

In accordance with U. S. Pat. No. 3,647,437, a lightabsorbing material or reagent, preferably a dye, is provided so positioned and/or constituted as not to interfere with photoexposure but so positioned between the photoexposed silver halide emulsions and the transparent support during processing after photoexposure as to light which otherwise might fog the photoexposed emulsions. Furthermore, the light-absorbing material is so positioned and/or constituted after processing as not to interfere with viewing the desired image shortly after said image has been formed. In the preferred embodiments, the light-absorbing material, also sometimes referred to herein as an optical filter agent, is initially contained in the processing composition together with a light-reflecting material, e.g., titanium dioxide.

The concentration of indicator dye is selected to provide the optical transmission density required, in combination with other layers intermediate the silver halide emulsion layer(s) and the incident radiation, to prevent nonimagewise exposure, i.e., fogging, by incident actinic light during the performance of the particular photographic process.

In lieu of having the reflecting pigment contained in the processing composition, e.g., as disclosed in the aforementioned copending applications, the reflecting pigment needed to mask the photosensitive strata and to provide the requisite background for viewing the color transfer image formed in the receiving layer may be contained initially in whole or in part as a preformed layer in the film unit. As an example of such a preformed layer, mention may be made of that disclosed in U. S. Pat. Nos. 3,615,421 issued Oct. 26, 1971 and 3,620,724 issued Nov. 16, 1971 of Edwin H. Land. The reflecting pigment may be generated in situ as is disclosed in the copending applications of Edwin [-1. Land, Ser. No. 43,741, now US. Pat. No. 3,647,434, and 43,742, now U.S. Pat. No. 3,647,435, both filed June 5, 1970.

Opacifying means may be provided on either side of the negative component so that the film unit may be processed in the light to provide the desired color transfer image. In a particularly useful embodiment such opacifying means comprise an opaque dimensionally stable layer or support member positioned on the free or outer surface of the negative component, i.e., on the surface of the film unit opposed from the positive component containing the dyeable stratum to prevent photoexposure by actinic light incident thereon from this side of the film unit and an opacifying agent applied during development between the dyeable stratum and the negative component, e.g., by including the opacifying agent in a developing composition so applied, in order to prevent further exposure (fogging) by actinic light incident thereon from the other side of the film unit when the thus exposed film unit is developed in the light. The last-mentioned opacifying agent may comprise the aforementioned reflecting agent which masks the negative component and provides the requisite background for viewing the transfer image formed thereover. Where this reflecting agent does not by itself provide the requisite opacity it may be employed in combination with an additional opacifying agent in order to prevent further exposure of the light-sensitive silver halide layer or layers by actinic light incident thereon.

As examples of such integral negative-positive film units for preparing color transfer images viewable without separation as reflection prints, mention may be made of those described and claimed in U. S. Pat. Nos. 3,415,644; 3,415,645; 3,415,646; 3,473,925; 3,573,043; 3,576,625; 3,573,042; 3,594,164; and 3,594,165.

U. S. Pat. No. 3,579,333, issued May 18, 1971, is directed to film units of the above-described type which includes a silver halide desensitizing agent adapted to effect, subsequent to photoexposure, desensitization of the photosensitive silver halide layer without substantial detriment to the latent image carried by the emulsion layer, to permit the film unit to be processed externally to the camera in which it was'exposed.

1n the various color diffusion transfer systems which have previously been described and which employ an aqueous alkaline processing fluid, it is well known to employ an acid-containing layer to lower the environmental pH following substantial dye transfer in order to increase the image stability and/or to adjust the pH from a first pH at which the imaging dyes are diffusible to a second (lower) pH at which they are not. For example, U. S. Pat. No. 3,362,819 discloses sytems wherein the desired pH reduction may be effected by providing a polymeric acid layer adjacent the dyeable stratum. These polymeric acids may be polymers which contain acid groups, e.g., carboxylic acid and sulfonic acid groups, which are capable of forming salts with al kali metals or with organic bases; or potentially acidyielding groups such as anhydrides or lactones. Preferably the acid polymer contains free carboxyl groups. As examples of other useful neutralizing layers, in addition to those disclosed in the aforementioned U. S. Pat. No. 3,362,819, mention may be made of those disclosed in the following copending applications: Ser. No. '1 65,171 of Schlein et al., filed July 22, 1971; Ser. No. 214,746 of Bedell, filed Jan. 3, 1972; Ser. No. 208,616 of Taylor, filed Dec. 16, 1971; Ser. No. 231,835 of Sahatjian et al., filed Mar. 6, 1972, etc.

. An inert interlayer or spacer layer may be and is preferably disposed between the polymeric acid layer and the dyeable stratum in order to control the pH reduction so that it is not premature and hence interferes with the development process, e.g., to time control the pH reduction. Suitable spacer or timer layers for this purpose are described with particularity in U.S. Pat. No. 3,362,819 and in others, including U. S. Pat.

Nos. 3,419,389; 3,421,893; 3,433,633; 3,455,686; and 3,575,701.

While the acid layer and associated spacer layer are preferably contained in the receiving element employed in systems wherein the dyeable stratum and photosensitive strata are contained on Separate elements, e.g., between the support for the receiving element and the dyeable stratum; or associated with the dyeable stratum in those integral film units, e.g., on the side of the dyeable stratum opposed from the negative component, they may, if desired, be associated with the photosensitive strata, as is disclosed, for example, in U. S. Pat. Nos. 3,362,821 and 3,573,043. In film units such as those described in the aforementioned U. S. Pat. Nos. 3,594,164 and 3,594,165, they also may be contained on the spreader sheet employed to facilitate application of the processing fluid.

SUMMARY OF THE INVENTION The present invention is directed to a new and improved, preferably integral negative/positive, diffusion transfer process photographic film unit adapted to provide, by diffusion transfer processing, photographic color image reproduction as a function of exposure of such film unit to incident actinic radiation.

The film unit assemblage construction to be empioyed in the practice of the present invention preferably comprises a film unit of the general type set forth in aforementioned U. S. Pat. Nos. 3,415,644; 3,415,645; and 3,415,646, 3,473,925; 3,573,042; 3,573,043; 3,573,044; and copending U. S. Patent applications Ser. Nos. 786,352 now abandoned; 3691 now abandoned; 43,741 now Uv S. Pat. No. 3,647,439; 43,742, now US. Pat. No. 3,647,435; and 43,782 now abandoned and also in U. S. Pat. Nos. 3,615,421; 3,576,625; 3,576,626; 3,620,724; 3,594,165; 3,594,164; 2,983,606; and 3,345,163; and will include a photosensitive silver halide layer having associated therewith an effective amount of a substantially colorless, photographically inactive precursor of an alkyl viologen dye wherein said precursor is adapted to be converted to an alkyl viologen dye, subsequent to exposure, disposed in a photosensitive element which contains a plurality of layers including, in relative order, a dimensionally stable layer preferably opaque to incident actinic radiation; and one or more photosensitive silver halide layers having associated therewith dye image-forming material which is processing composition diffusible as a function of the point-to-point degree of silver halide layer exposure to incident actinic radiation; a layer adapted to receive image-forming material diffusing thereto; a dimensionally stable layer transparent to incident actinic radiation; and means for interposing, intermediate the silver halide layers and the reception layer, a reflecting agent and a processing composition, and, in a particularly preferred embodiment, a processing composition possessing a first pH at which the dye image-forming material is diffusible during processing an means for modulating the pH of the film unit from the first pH to a second pH at which the dye image-forming material is substantially non-diffusible subsequent to substantial dye transfer image formation.

In accordance with a specifically preferred embodiment of the present invention, a film unit assemblage of the aforementioned general structural parameters will be adapted to be processed, subsequent to photoexposure, in the presence of actinic radiation and may be fabricated to empioy, as means interposed intermediate the reception layer and next adjacent silver halide layer subsequent to photoexposure, an inorganic lightreflecting pigment dispersion containing reflecting pigment and, optionally, and optical filter agent, at a pH above the pKa of the optical filter agent and at which pH the dye image-forming material is diffusible during processing as a function of silver halide layer photoexposure, in a concentration in admixture effective to provide a barrier to transmission of actinic radiation therethrough, and the means for interposing the processing composition may comprise a rupturable container, retaining the opacifying agent, if any, disposed in the processing composition selected, fixedly positioned extending transverse a leading edge of the film unit and adapted, upon application of compressive pressure, to distribute its contents intermediate the reception layer and next adjacent silver halide layer. By employing the above-described precursor, the optical filter agent may be omitted from the film unit.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a perspective view of a photographic film unit embodying the invention;

FIGS. 2, 4 and 6 are diagrammatic enlarged crosssectional views of the film unit of FIG. 1, along section line 2-2, illustrating the association of elements during the three illustrated stages of the performance of a diffusion transfer process, for the production of a multicolor transfer image according to the invention, the thickness of the various materials being exaggerated, and wherein FIG. 2 represents an exposure stage, FIG. 4 represents a processing stage and FIG. 6 represents a product of the process; and

FIGS. 3, 5 and 7 are diagrammatic, further enlarged cross-sectional views of the film unit of FIGS. 2, 4 and 6, along section lines 33, 5-5 and 77, respectively, further illustrating, in detail, the arrangement of layers comprising the photosensitive laminate during the three illustrated stages of the transfer process.

DETAILED DESCRIPTION OF THE INVENTION In accordance with this invention, a substantially col orless precursor of an alkyl viologen dye is provided to the photosensitive element, positioned intermediate the silver halide emulsion layer and a transparent support so that subsequent to photoexposure of the silver halide emulsion, methyl-viologen dye can be generated in situ so as to absorb light which otherwise might fog the photoexposed emulsions and/or desensitize the silver halide grains. Preferably, the precursor is disposed adjacent or in the silver halide emulsion layer. Thus, unlike the preferred embodiments of U. S. Pat. No. 3,647,437, the light-absorbing material is not disposed in the processing composition where it might interact deleteriously with some of the photographic reagents contained therein.

As well as being colored, alkyl viologen is also a silver halide desensitizing agent. Thus, in addition to a light filtering mechanism, a silver halide desensitizing mechanism may also be employed to protect the silver halide emulsion layer from post-exposure fogging. While the two described functions can be performed simultaneously, it should be understood that the quantity employed is generally much less to achieve silver halide desensitization than for the filtering effect; and, in fact, an amount sufficient to provide desensitization may not provide sufficient filtering to prevent postexposure fogging.

The term silver halide desensitizing agent precursor" is intended to refer to a compound which is initially inert with respect to the desensitizing function and substantially colorless until the desensitizing function is generated by the action of alkali subsequent to exposure.

The alkyl viologen precursor may be represented by the formulae:

wherein R and R each are alkyl groups, preferably 15 carbon alkyl groups, more preferably methyl groups, and X is an acid anion, preferably a halide. It should be understood that the rings may optionally be substituted by one or more groups that are not photographically deleterious, e.g., alkyl, alkoxy, phenyl, sulfonyl, sulfonamide and carboxyl groups.

As stated above, the alkyl viologen precursor is a compound which does not deleteriously effect the photographic response of the silver halide grains but which can be converted to an alkyl viologen which will prevent post-exposure fogging of the photographic silver halide. The aforementioned conversion is accomplished by contacting the precursor with the processing composition which contains aqueous alkali.

The reactions employed in forming methyl viologen are represented below:

Substantially colorless and Colored and a strong desensitlzer and Substantially colorless and not a. desensitlzer CH3N WN-Clla V Colored and a strong desensltizar In the present invention, a normally inert and substantially colorless compound is disposed in or near a photosensitive silver halide layer. In its inert form, the compound will not have any effect on the composition, exposure or processing of the silver halide emulsion until the emulsion layer is contacted with an alkaline processing composition which generates the alkyl viologen dye.

In one embodiment, the concentration of precursor is selected to provide sufficient alkyl viologen dye having the optical transmission density required, in combination with other layers intermediate the silver halide emulsion layer(s) and the incident radiation, to prevent nonimagewise exposure, i.e., fogging, by incident actinic light during the performance of the particular photographic process. It has been found, by interposing neutral density (carbon containing) filters over a layer of-titanium dioxide, that a transmission density of approximately 6.0 from said neutral density filters are effective to prevent fogging of a diffusion transfer multicolor film unit of the type described in said U. S. Pat. No. 3,415,644 having a transparent support layer and an Equivalent ASA Exposure Index of approximately 75 when processed for one minute in 10,000 foot candles of color-corrected light, a light intensity approximately the intensity of a noon summber sun. The transmission density required to protect such a film unit under the stated conditions may also be expressed in terms of the system transmission density of all the layers intermediate the silver halide layer(s) and the incident light, the system transmission density required to protect a color film unit of the aforementioned type and photographic speed has been found to be on the order of 7.0 to 7.2. Lesser levels of optical transmission density would, of course, provide effective protection for shorter processing times, lesser light intensities and/or films having lower exposure indices. The transmission density and the dye concentration necessary to provide the requisite protection from incident light may be readily determined for any photographic process by following the above-described procedure or obvious modifications thereof. It will be recognized that a particular transmission density may not be required for all portions of thespectrum, lesser density being sufficient in wavelength regions corresponding to lesser sensitivities of the particular photosensitive material.

It should also be understood that an optical filter agent, as described in U. S. Pat. No. 3,647,437, may be employed in conjunction with the precursor of the present invention. A relatively small amount need be employed, however, since the combined effect of the optical filter agent and the methylviologen formed from the precursor will provide the necessary light protective properties.

The silver halide photosensitive layers employed for the fabrication of the photographic film unit, may be prepared by reacting a water-soluble silver salt, such as rial, by chilling the dispersion, noodling the set dispersion, and washing the noodles with cold water, or, alternatively, employing any of the various flocc systems, or procedures, adapted to effect removal of undesired components, for example, the procedures described in U. S. Pat. Nos. 2,614,928; 2,614,929; 2,728,662, and the like; afterripening the dispersion at an elevated temperature in combination with the addition of gelatin or such other polymeric material as may be desired and various adjuncts, for example, chemical sensitizing agents of U. S. Pat. Nos. 1,574,944; 1,623,499; 2,410,689; 2,597,856; 2,597,915; 2,487,850; 2,518,698; 2,521,926; and the like; all according to the traditional procedures of the art, as described in Neblette, C. 13., Photography its Materials and Processes, 6th Ed, 1962.

Optical sensitization of the emulsions silver iodochlorobromide crystals may be accomplished by con tact of the emulsion composition with an effective concentration of the selected optical sensitizing dyes dissolved in an appropriate dispersing solvent such as methanol, ethanol, acetone, water, and the like; all according to the traditional procedures of the art, as described in Hammer, F. M., The Cyanine Dyes and Related Compounds.

Additional optional additives, such as coating aids, hardeners, viscosity-increasing agents, stabilizers, preservatives, and the like, for example, those set forth hereinafter, also may be incorporated in the emulsion formulation, according to the conventional procedures known in the photographic emulsion manufacturing art.

As the binder for the photoresponsive material, the aforementioned gelatin may be, in whole or in part, replaced with some other natural and/or synthetic processing composition permeable polymeric material such as albumin; casein; or zein or resins such as cellulose derivative, as described in U. S. Pat. Nos. 2,322,085 and 2,541,474; vinyl polymeric such as described in an extensive multiplicity of readily available U. S. and foreign patents or the photoresponsive mate rial may be present substantially free of interstitial binding agent as described in U. S. Pat. Nos. 2,945,771; 3,145,566; 3,142,567; Newman, Comment on Non- Gelatin Film, B. J. O. P., 434, Sept. 15, 196i; and Belgian Pat. Nos. 642,557 and 642,558.

As previously mentioned, photosensitive silver iodochlorobromide emulsions possessing the preformed grain size distribution may be readily obtained by a plurality of conventional emulsion manufacturing procedures known to those skilled in the art, including procedures and apparatus particularly adapted to provide restricted and substantially homogeneous or uniform grain size distributions; see, for example, the processes and apparatus disclosed in U. S. Pat. Nos. 3,326,641 and 3,415,650, each of which is specifically hereby incorporated herein by reference.

Reference is now made to FIGS. 1 through 7 of the drawings wherein there is illustrated a preferred film unit of the present invention and wherein like numbers, appearing in the various figures, refer to like components.

As illustrated in the drawings, FIG. 1 sets forth a per spective view of the film unit, designated 10, and each of FIGS. 2 through 7 illustrate diagrammatic crosssectional views of film unit 10, along the stated section lines 2-2, 3-3, 55 and 7-7, during the various depicted stages in the performance of a photographic diffusion transfer process as detailed hereinafter.

Film unit 10 comprises rupturable container 11, retaining, prior to processing, aqueous processing composition 12, and photosensitive laminate 13 including, in order, dimensionally stable opaque layer 14, preferably an actinic radiation-opaque flexible sheet material; cyan dye developer layer 15; red-sensitive silver iodochlorobromide emulsion layer 16; interlayer l7; magenta dye developer layer 18; green-sensitive silver iodochlorobromide emulsion layer 19; interlayer 20; yellow dye developer layer 21; blue-sensitive silver iodochlorobromide emulsion layer 22; auxiliary layer 23, which may contain an auxiliary silver halide devel oping agent; image-receiving layer 24; spacer layer 25; neutralizing layer 26; and dimensionally stable transparent layer 27, preferably an actinic radiation transmissive flexible sheet material.

The structural integrity of laminate 13 may be maintained, at least in part, by the adhesive capacity exhibited between the various layers comprising the laminate at their opposed surfaces. However, the adhesive capacity exhibited at an interface intermediate imagereceiving layer 24 and the silver iodochlorobromide emulsion layer next adjacent thereto, for example, image-receiving layer 24 and auxiliary layer 23 as illustrated in FIGS. 2 through 7, should be less than that exhibited at the interface between the opposed surfaces of the remainder of the layers forming the laminate, in order to facilitate distribution of processing solution 12 intermediate the stated image-receiving layer 24 and the silver iodochloro-bromide emulsion layer next adjacent thereto. The laminates structural integrity may also be enhanced or provided, in whole or in part, by providing a binding member extending around, for example, the edges of laminate l3, and maintaining the layers comprising the laminate intact, except at the interface between layers 23 and 24 during distribution of processing composition 12 intermediate those layers. As illustrated in the figures, the binding member may comprise a pressure-sensitive tape 28 securing and/or maintaining the layers of laminate 13 together at its respective edges. Tape 28 will also act to maintain processing solution 12 intermediate image-receiving layer 24 and the silver iodochlorobromide emulsion layer next adjacent thereto, upon application of compressive pressure to pod 11 and distribution of its contents intermediate the stated layers. Under such circumstances, binder tape 28 will act to prevent leakage of fluid processing composition from the film units laminate during and subsequent to photographic processing.

Rupturable container 11 may be of the type shown and described in any of U. S. Pat. Nos. 2,543,181; 2,634,886; 3,653,732; 2,723,051; 3,056,492; 3,056,491; 3,152,515; and the like. In general, such containers will comprise a rectangular blank of fluidand air-impervious sheet material folded longitudinally upon itself to form two walls 29 which are sealed to one another along their longitudinal and end margins to form a cavity in which processing composition 12 is retained. The longitudinal marginal seal 30 is made weaker than the end seals 3i so as to become unsealed in response to the hydraulic pressure generated within the fluid contents 12 of the container by the application of compressive pressure to walls 29 of the container.

As illustrated in FIGS. 1, 2 and 3, container 11 is fixedly positioned and extends transverse a leading edge of photosensitive laminate 13 whereby to effect unidirectional discharge of the containers contents 12 between image-receiving layer 24 and the stated layer next adjacent thereto, upon application of compressive force to container 11. Thus, container 11, as illustrated in FIG. 2, is fixedly positioned and extends transverse a leading edge of laminate 13 with its longitudinal marginal seal 30 directed toward the interface between image-receiving layer 24 and auxiliary layer 23. As shown in FIGS. 1, 2 and 4, container 11 is fixedly secured to laminate 13 by extension 32 of tape 28 extending over a portion of one wall 29 of the container, in combination with a separate retaining member such as illustrated retaining tape 33 extending over a portion of laminate 13s surface generally equal in area to about that covered by tape 28.

As illustrated in FIGS. 1, 2 and 4, extension flap 32 of tape 28 is preferably of such area and dimensions that upon, for example, manual separation of container 11 and tape 33, subsequent to distribution of processing composition 12, from the remainder of film unit 10, flap 32 may be folded over the edge of laminate 13, previously covered by tape 33, in order to facilitate maintenance of the laminates structural integrity, for example, during the flexations inevitable in storage and use of the processed film unit, and to provide a suitable mask or frame, for viewing of the transfer image through the picture viewing area of transparent layer.

The fluid contents of the container preferably comprise an aqueous alkaline solution having a pH and solvent concentration at which the dye developers are soluble and diffusible and contains inorganic light reflecting pigment. By virtue of the methylviologen, as well as an optional optical filter agent, the film unit may be processed, subsequent to distribution of the composition, in the presence of such radiation, in view of the fact that the silver iodochlorobromide emulsion or emulsions of laminate are appropriately desensitized and protected from incident radiation.

The selected reflecting pigment should be one providing a background suitable for viewing the dye developer transfer image formed in the dyeable polymeric layer. In general, while substantially any reflecting agent may be employed, it is preferred that a reflecting agent be selected that will not interfere with the color integrity of the dye transfer image, as viewed by the observer, and, most preferably, an agent which is aesthetically pleasing to the viewer and does not provide a background noise signal degrading, or detracting from, the information content of the image. Particularly desirable reflecting agents will be those providing a white background, for viewing the transfer image, and specifically those conventionally employed to provide background for reflection photographic prints and, especially those agents possessing the optical properties desired for reflection of incident radiation.

As examples of reflecting pigments adapted for employment in the practice of the present invention, mention may be made of barium sulfate, zinc sulfide, titanium dioxide, barium stearate, silver flake, silicates, alumina, zirconium oxide, zirconium acetyl acetate, sodium zirconium sulfate, kaolin, mica, and the like.

A particularly preferred reflecting agent comprises titanium dioxide due to its highly effective reflection properties. In general, in such preferred embodiment, based upon percent titanium dioxide (weight/volume) a processing composition containing about 1,500 to 4,000 mgs./ft. titanium dioxide dispersed in 100 cc. of water will provide a percent reflectance of about to percent. In the most preferred embodiments, the percent reflectance particularly desired will be in the order of about 85 percent.

In embodiments wherein the dispersion comprises a preformed layer positioned intermediate the reception layer and next adjacent silver iodochlorobromide layer, the pigment layer will be sufficiently transparent to allow transit of exposing radiation through the pigment layer and may comprise titanium dioxide reflecting agent possessing a particle size distribution averaging about 0.2 u in diameter and preferably about 0.05 ,u. in diameter as initially present preceding exposure of the film unit, which preferred materials, upon contact with aqueous alkaline processing composition, preferably aggregate to provide particles possessing a diameter about 0.2 ,u. in diameter and will be coated at a coverage of about 200 to 1,000 mgs./ft. Specifically, the reflecting agent will be present in a quantity insufficient to prevent exposure of the emulsion layers by actinic radiation incident on the dimensionally stable transparent layer of the film unit but in a concentration sufficient, subsequent to processing, to mask dye developer associated with the silver iodochlorobromide emulsion strata from the dye transfer image. In the preferred construction of such embodiment, the pigment such as titanium dioxide will be initially present in a relatively small particle size to provide unexpectedly efficient transit of radiation through the reflecting layer during exposure which upon contact with an alkaline processing composition and aggregation of the pigment particles provides efficient light reflectivity and masking capacity subsequent to such aggregation.

In general, the reflecting agents to be employed are those which remain substantially immobile within their respective compositions during and subsequent to photographic processing and particularly those which comprise insoluble and nondiffusible inorganic pigment dispersions within the layer in which they are disposed.

Where desired, reflecting agent pigment may thus be distributed in whole or in part within a processing composition permeable polymeric matrix such as gelatin and/or any other such polymeric matrixes as are specifically denoted throughout the specification as suitable for employment as a matrix binder and may be distributed in one or more of the film unit layers which may be separated or contiguous, intermediate the imagereceiving layer and next adjacent silver halide layer, provided that its distribution and concentration is effective to provide the denoted post processing masking function, and/or in whole or in part the reflecting agent may be ultimately disposed within the processing composition residuum located intermediate the imagereceiving layer and next adjacent silver halide emulsion strata and associated dye image-forming material.

If an optical filter agent is employed, the agent selected should be one exhibiting, at a pH above its pKa,

maximum spectral absorption of radiation at the wavelengths to which the film units photosensitive silver halide layer or layers are sensitive and should be substantially immobile or nondiffusible within the pigment dispersion, during performance of its radiation filtration function, in order to maintain and enhance the optical integrity of the dispersion as a radiation filter unit functioning in accordance with the present invention, and

to prevent its diffusion into and localized concentration within the image-receiving layer thereby decreasing the efficiency of the reflecting pigment dispersion as a background against which image formation may be immediately viewed, during the initial stages in the diffusion transfer processing of the film unit, by filter agent absorption of dispersion reflected visible radiation prior to reduction in the environmental pH below the pKa of the agent.

As specific examples of such pH-sensitive optical fil ter agents adapted for employment in the practice of the present invention, reference is directed to the agents set forth in aforementioned copending U. S. patent application Ser. No. 43,782, filed June 5, 1970, incorporated herein by reference.

In general, preferred agents, both opacifying and filter, are those which remain immobile within their respective compositions during and subsequent to photographic processing and particularly those which comprise insoluble and nondiffusible materials.

As disclosed in the previously cited patents, the liquid processing composition referred to for effecting multicolor diffusion transfer processes comprises at least an aqueous solution of an alkaline material, for example, diethylamine, sodium hydroxide or sodium carbonate and the like, and preferably possessing a pH in excess of l2, and most preferably includes a viscosity-increasing compound constituting a film-forming material of the type which, when the composition is spread and dried, forms a relatively firm and relatively stable film. The preferred film forming materials disclosed comprise high molecular weight polymers such as polymeric, water-soluble ethers which are inert to an alkaline solution such as, for example, a hydroxyethyl cellulose or sodium carboxymethyl cellulose. Additionally, film-forming materials or thickening agents whose ability to increase viscosity is substantially unaffected if left in solution for a long period of time are also disclosed to be capable of utilization. As stated, the filmforming material is preferably contained in the processing composition in such suitable quantities as to impart to the composition a viscosity in excess of 100 cps. at a temperature of approximately 24 C. and preferably in the order of 100,000 cps. to 200,000 cps. at that temperature.

In the performance of a diffusion transfer multicolor process employing film unit 30, the unit is exposed to radiation, actinic to photosensitive laminate l3, incident on the laminates exposure surface, as illustrated in FIG. 3.

Subsequent to exposure, as illustrated by H68. 2 and 4, film unit 10 is processed by being passed through opposed suitably gapped rolls 35 in order to apply compressive pressure to frangible container 11 and to effect rupture of longitudinal seal 30 and distribution of alkaline processing composition 12, possessing inorganic light-reflecting pigment and the optional optical filter agent at a pH above the pKa of the filter agent and a pH at which the cyan, magenta and yellow dye developers are soluble and diffusible as a function of the pointto-point degree of exposure of red-sensitive silver iodochlorobromide emulsion layer 16, green-sensitive silver iodochlorobromide emulsion layer 19 and bluesensitive silver iodochlorobromide emulsion layer 22, respectively, intermediate image-receiving layer 24 and auxiliary layer 23.

Alkaline processing composition 12 permeates emulsion layers l6, l9 and 22 to initiate development of the latent images contained in the respective emulsions. The cyan, magenta and yellow dye developers, of layers 15., 18 and 21, are immobilized, as a function of the development of their respective associated silver iodochlorobromide emulsions, preferably substantially as a result of their conversion from the reduced form to their relatively insoluble and nondiffusible oxidized form, thereby providing imagewise distributions of mobile, soluble and diffusible cyan, magenta and yellow dye developer, as a function of the point-to-point degree of their associated emulsions exposure. At least part of the imagewise distributions of mobile cyan, magenta and yellow dye developer transfers, by diffusion, to dyeable polymeric layer 24 to provide a multicolor dye transfer image to that layer which is viewable against the background provided by the reflecting pigment present in processing composition residuum 12 masking cyan, magenta and yellow dye developer remaining associated with blue-sensitive emulsion layer 22, green-sensitive emulsion layer 19 and red-sensitive emulsion layer 16. Subsequent to substantial transfer image formation, a sufficient portion of the ions comprising aqueous alkaline processing composition 12 transfer, by diffusion, through permeable polymeric reception layer 24, permeable spacer layer 25 to polymeric neutralizing layer 26 whereby the environmental pH of the system decreases as a function of neutralization to a pH at which the cyan, magenta and yellow dye developers, in the reduced form, are substantially nondiffusible to thereby provide a stable multicolor dye transfer image and discharge of the pH-sensitive optical filter agent by reduction of the pH substantially below the pKa of such agent to thereby provide maximum reflectivity in terms of the pigment concentration prescut.

The alkaline solution component of the processing composition, positioned intermediate the photosensitive element and the image-receiving layer, thus permeates the emulsions to initiate development of the latent images contained therein. The respective associated dye developers are mobilized in unexposed areas as a consequence of the development of the latent images. This mobilization is apparently, at least in part, due to a change in the solubility characteristics of dye developer upon oxidation and especially as regards its solubility in alkaline solutions. It may also be due in part to a tanning effect on the emulsion by oxidized developing agent, and in part to a localized exhaustion of alkali as a result of development. in unexposed and partially exposed areas of the emulsions, the associated dye developer is diffusible and thus provides an imagewise distribution of unoxidized dye developer dissolved in the liquid processing composition, as a function of the pointto-point degree of exposure of the silver iodochlorobromide emulsion. At least part of this imagewise distribution of unoxidized dye developer is transferred, by imbibition, to a superposed image-receiving layer or element, said transfer substantially excluding oxidized dye developer. The image-receiving element receives a depthwise diffusion, from the developed emulsion, of unoxidized dye developer without appreciably disturbing the imagewise distribution thereof to provide the reversed or positive color image of the developed image.

Subsequent to distribution of processing composition 12, container 11 may be manually dissociated from the remainder of the film unit, as described above, to provide the product illustrated in FIG. 6.

The present invention will be further illustrated and detailed in conjunction with the following illustrative constructions which set out representative embodiments and photographic utilization of the novel photographic film units of this invention, which, however, are not limited to the details therein set forth and are intended to be illustrative only.

Film units similar to that shown in the drawings may be prepared, for example, by coating, in succession, on a 5 mil. opaque polyester film base, the following layers:

l. a layer of the cyan dye developer HO-CHz-CHz dispersed in gelatin and coated at a coverage of about 71 mgsJt't. of dye and about 50 mgsJft. of gelatin;

5. a green-sensitive geIatino-silver iodochlorobromide emulsion coated at a coverage of about mgs./ft. of silver and 40 mgsJft. of gelatin;

6. a layer comprising butyl acrylate/diacetone acrylamide/styrene/methacrylic acid (60/30/4/6) and polyacrylamide coated in a ratio of about 29:4, respectively, at a coverage of about 60 mgs./ft.

7. a layer of the yellow dye developer O OH and the auxiliary developer 4'-methylphenyl hydroquinone dispersed in gelatin and coated at a coverage of about 81 mgsJft. of dye, about 15 mgs./ft. of auxiliary developer and 54 mgs./ft. of gelatin;

8. a blue-sensitive gelatino-silver iodochlorobromide emulsion coated at a coverage of about 65 mgs./ft. of silver and about 33 mgs./ft. of gelatin; and

9. a layer to be described below.

Then a transparent 5 mil. polyester film base may be coated, in succession, with the following illustrative layers:

The two components thus prepared may then be taped together in laminate form, at their respective edges, by means of a pressure-sensitive binding tape extending around, in contact with, and over the edges of the resultant laminate.

A rupturable container comprising an outer layer of --lead foil and an inner liner or layer of polyvinyl chloride retaining an aqueous alkaline processing solution comprising:

Water 100.0 cc Potassium hydroxide 7.5 g

Carboxymethyl cellulose sodium salt 3. N-phenethyl-a-picolinium bromide l Cesium hydroxide Benzotriazole L g. 6-bromo-5-methyl-4 azabenzimidazole 0.05 g. Titanium dioxide 50.0 g. Z-methylimidazole 0.35 g.

may then be fixedly mounted on the leading edge of each of the laminates, by pressure-sensitive tapes interconnecting the respective containers and laminates, such that, upon application of compressive pressure to a container, its contents may be distributed, upon rupture of the containers marginal seal, between the polymeric image-receiving layer and next adjacent layer.

The precursors of the present invention may be introduced into the film by applying a 0.1 percent solution in gelatin over the negative with a No. 5 Meyer Rod in forming the above-indicated layer 9. Alternatively, the precursors may bedissolved in water with a wetting agent and coated directly over layer 8. In still another alternative, the precursors are disposed in one or more of the silver halide emulsion layers. Amounts ranging from 5 to 250 mgs. may be employed. A control was also prepared wherein layer 9 comprised 30 mgs./ft. gelatin.

The photosensitive composite film units may be ex posed to radiation incident on the transparent cellulose triacetate layer through a conventional step wedge and processed by passage of the exposed film units through appropriate pressure-applying members, such as suitable gapped, opposed rolls, to effect rupture of the container and distribution of its contents. Subsequent to processing, the multicolor dye transfer image formation may be viewed through the transparent polyester layer against the titanium dioxide background provided by distribution of the pigment containing processing composition between layer 9 and the polymeric imagereceiving layer. Multicolor dye transfer image formation was examined in comparison with controls after imbibition in the dark for periods of 10 seconds and 10 minutes, To evaluate the effect of the alkyl viologen, the pH dependent optical filter agents were omitted from the processing reagent.

Neutralizing means, for example, a polymeric acid layer of the type discussed above may be incorporated, as stated, in the film unit of the present invention, to provide reduction of the alkalinity of the processing solution from a pH above the pKa of the optical filter agent selected at which the dyes are soluble to a pH below the pKa of the agent at which the dyes are substantially nondiffusible, in order to advantageously further stabilize and optimize reflectivity of the dye transfer image. In such instance, the neutralizing layer may comprise particulate acid reacting reagent disposed within the film unit or a polymeric acid layer, for example, a polymeric acid layer approximating 0.3 to 1.5 mils. in thickness, positioned intermediate the transparent support and image-receiving layer, and/or the opaque support and next adjacent emulsion/dye unit layer, and the film unit may also contain a polymeric spacer or barrier layer, for example, approximating 0.1 to 0.7 mil. in thickness, next adjacent the polymeric acid layer, opposite the respective support layer, as previously described.

Specifically, the film units may employ the presence of a polymeric acid layer such as, for example, of the type set forth in U. S. Pat. No. 3,362,819 which, most preferably, includes the presence of an inert timing or spacer layer intermediate the polymeric acid layer carried on a support and the image-receiving layer.

As set forth in the last-mentioned patent, the polymeric acid layer may comprise polymers which contain acid groups, such as carboxylic acid and sulfonic acid groups, which are capable of forming salts with alkali metals, such as sodium, potassium etc., or with organic bases, particularly quaternary ammonium bases, such as tetramethyl ammonium hydroxide, or potentially acid-yielding groups, such as anhydrides or lactones, or other groups which are capable of reacting with bases to capture and retain them. The acid-reacting group is, of course, retained in the polymer layer. In the preferred embodiments disclosed, the polymer contains free carboxyl groups and the transfer processing composition employed contains a large concentration of sodium and/or potassium ions. The acid polymers stated to be most useful are characterized by containing free carboxyl groups, being insoluble in water in the free acid form, and by forming water-soluble sodium and/or potassium salts. One may also employ polymers containing carboxylic acid anhydride groups, at least some of which preferably have been converted to free carboxyl groups prior to imbibition. While the most readily available polymeric acids are derivatives of cellulose or of vinyl polymers, polymeric acids from other classes of polymers may be used. As examples of specific polymeric acids set forth in the application, mention may be made of dibasic acid half-ester derivatives of cellulose which derivatives contain free carboxyl groups, e.g., cellulose acetate hydrogen phthalate, cellulose acetate hydrogen glutarate, cellulose acetate hydrogen succinate, ethyl cellulose hydrogen succinate, ethyl cellulose acetate hydrogen succinate, cellulose acetate hydrogen succinate hydrogen phthalate; ether and ester derivatives or cellulose modified with sulfoanhydrides, e.g., with ortho-sulfobenzoic anhydride; polystyrene sulfonic acid; carboxymethyl cellulose; polyvinyl hydrogen phthalate; polyvinyl acetate hydrogen phthalate; polyacrylic acid; acetals of polyvinyl alcohol with carboxy or sulfo substituted aldehydes, e.g., o, rn-, or pbenzaldehyde sulfonic acid or carboxylic acid; partial esters of ethylene/maleic anhydride copolymers; partial esters of methyl-vinyl ether/maleic anhydride copolymers; etc.

in order to prevent premature pl-l reduction during transfer processing, as evidenced, for example, by an undesired reduction in positive image density, the acid groups are disclosed to be so distributed in the polymer layer that the rate of their availability to the alkali is controllable, e.g., as a function of the rate of swelling of the polymer layer which rate in turn has a direct relationship to the diffusion rate of the alkali ions. The desired distribution of the acid groups in the polymer layer may be effected by mixing acid polymer with a polymer free of acid groups, or lower in concentration of acid groups, and compatible therewith, or by using only an acid polymer but selecting one having a relatively lower proportion of acid groups. These embodiments are illustrated, respectively, in the cited copending application, by (a) a mixture of cellulose acetate and cellulose acetate hydrogen phthalate and (b) a cellulose acetate hydrogen phthalate polymer having a much lower percentage of phthayl groups than the firstrnentioned cellulose acetate hydrogen phthalate.

It is also there disclosed that the layer containing the polymeric acid may contain a water-insoluble polymer, preferably a cellulose ester, which acts to control or modulate the rate at which the alkali salt of the polyany given embodiment are, of course, selected so as to have adequate wet and dry strength and when necessary or desirable, suitable subcoats are employed to help the various polymeric layers adhere to each other during storage and use.

The inert spacer layer of the last-mentioned patent, for example, an inert spacer layer comprising polyvinyl alcohol or gelatin, acts to time control the pH reduction by the polymeric acid layer. This timing is disclosed to be a function of the rate at which the alkali diffuses through the inert spacer layer. It is there stated to have been found that the pH does not drop until the alkali has passed through the spacer layer, i.e., the pH is not reduced to any significant extent by the mere diffusion into the interlayer, but the pH drops quite rapidly once the alkali diffuses through the spacer layer.

As disclosed in aforementioned U. S. Pat. No. 3,362,819, the presence of an inert spacer layer was found to be effective in evening out the various reaction rates over a wide range of temperatures, for example, by preventing premature pl-l reduction when imbibition is effected at temperatures above room temperature, for example, at 95 to 100 F. By providing an inert spacer layer, that application discloses that the rate at which alkali is available for capture in the polymeric acid layer becomes a function of the alkali diffusion rates.

However, as disclosed in U. S. Pat. No. 3,455,686 preferably the aforementioned rate at which the cations of the alkaline processing composition, i.e., alkali ions, are available for capture in the polymeric acid layer should be decreased with increasing transfer processing temperatures in order to provide diffusion transfer color processes relatively independent of positive transfer image variations over an extended range of ambient temperatures.

Specifically, it is there stated to have been found that the diffusion rate of alkali through a permeable inert polymeric spacer layer increases with increased processing temperature to the extent, for example, that at relatively high transfer processing temperatures, that is, transfer processing temperatures above approximately 80 F., a premature decrease in the pH of the transfer processing composition occurs due, at least in part, to the rapid diffusion of alkali from the dye transfer environment and its subsequent neutralization upon contact with the polymeric acid layer. This was stated to be especially true of alkali traversing an inert spacer layer possessing permeability to alkali optimized to be effective with the temperature range of optimum transfer processing. Conversely, at temperatures below the optimum transfer processing range, for example, temperatures below approximately 40 F., the last-mentioned inert spacer layer was disclosed to provide an effective diffusion barrier timewise preventing effective traverse of the inert spacer layer by alkali having temperature depressed diffusion rates and to result in maintenance of the transfer processing environments high pH for such as extended time interval as to facilitate formation of transfer image stain and its resultant degradation of the positive transfer images color definition.

It is further stated in the last-mentioned U. S. Pat. No. 3,455,686 to have been found, however, that if the inert spacer layer of the print-receiving element is replaced by a spacer layer which comprises a permeable polymeric layer exhibiting permeability inversely dependent on temperature, that is, a polymeric filmforming material which exhibits decreasing permeability to solubilized alkali derived cations such as alkali metal and quaternary ammonium ions under conditions of increasing temperature, that the positive transfer image defects resultant from the aforementioned overextended pH maintenance and/or premature pH reduction are obviated.

As examples of polymers which are disclosed to exhibit inverse temperature-dependent permeability to alkali, mention may be made of: hydroxypropyl polyvinyl alcohol, polyvinyl methyl ether, polyethylene oxide, polyvinyl oxazolidone, hydroxypropyl methyl cellulose, isopropyl cellulose, partial acetals of polyvinyl alcohol such as partial polyvinyl butyral, partial polyvinyl formal, partial polyvinyl acetal, partial polyvinyl propional, and the like.

The last mentioned specified acetals of polyvinyl were stated to generally comprise saturated aliphatic hydrocarbon chains of a molecular weight of at least 1,000, preferably of about 1,000 to 50,000, possessing a degree of acetalation within about 10 to 30 percent, 10 to 30 percent, 20 to percent, and 10 to 40 percent, of the polyvinyl alcohol's theoretical polymeric hydroxy groups, respectively, and including mixed acetals where desired.

Where desired, a mixture of the polymers may be employed, for example, a mixture of hydroxypropyl methyl cellulose and partial polyvinyl butyral.

Employment of the detailed and preferred film units of the present invention, according to the herein described color diffusion transfer process, specifically provides for the production of a highly stable transfer image accomplished, at least in part, by effectively obviating the previously discussed disadvantages of the prior art products and processes, by in process adjustment of the environmental processing composition solvent and pH concentration from a solvent and pH concentration at which dye diffusion or transfer is operative to a solvent and pH concentration at which dye transfer is inoperative subsequent to substantial transfer image formation. The stable color transfer image is obtained irrespective of the fact that the film unit is maintained as an integral laminate unit during exposure, processing, viewing, and storage of the unit. Accordingly, by means of the present invention, multicolor transfer images may be provided over an extended processing temperature range which exhibit desired maximum and minimum dye transfer images densities; yellow, magenta and cyan dye saturation; red, green and blue hues; and color separation. These unexpected advantages are in addition to the manufacturing advantages obtained by reason of the present inventions integral color transfer film unit construction and which will be readily apparent from examination of the units parameters, that is, for example, advantages in more efficient utilization of fabricating materials and components, enhanced simplicity of film manufacture and camera design and construction, and more simplified and effectively controlled customer utilization of the unit. v

The dimensionally stable support layers referred to may comprise any of the various types of conventional opaque and transparent rigid or flexible materials possessing the requisite liquid impermeability and. preferably, the vapor transmissivity denoted above, and may comprise polymeric films of both synthetic types and those derived from naturally occurring products. Particularly suitable materials include aqueous alkaline solution impermeable, water vapor permeable, flexible polymeric materials such as vapor permeable polymeric films derived from ethylene glycol terephthalic acid, vinyl chloride polymers; polyvinyl acetate; polyamides; polymeth-acrylic acid methyl and ethyl esters; cellulose derivatives such as cellulose, acetate, triacetate, nitrate, propionate, butyrate, acetate-propionate, or acetate-butyrate; alkaline solution impermeable, water vapor permeable papers; crosslinked polyvinyl alcohol; regenerated cellulose; and the like.

As examples, of materials, for use as the imagereceiving layer, mention may be made of solution dyeable polymers such as nylon as, for example, N- methoxymethyl polyhexamethylene adipamide; partially hydrolyzed polyvinyl acetate; polyvinyl alcohol with or without plasticizers; cellulose acetate with filler as, for example, one-half cellulose acetate and one-half oleic acid; gelatin; and other materials of a similar nature. Preferred materials comprise polyvinyl alcohol or gelatin containing a dye mordant such as poly-4- vinylpyridine, as disclosed in U. S. Pat. No. 3,148,061, issued Sept. 8, 1964.

it will be noted that the liquid processing composition employed may contain an auxiliary or accelerating developing agent, such as p-methylaminophenol, 2,4- diarninophenol, p-benzylaminophenyl, hydroquinone, toluhydroquinone, phenylhydroquinone, 4'-methylphenylhydroquinone, etc. It is also contemplated to employ a plurality of auxiliary or accelerating developing agents, such as a 3-pyrazolidone developing agent and a benzenoid developing agent, as disclosed in U. S. Pat. No. 3,039,869, issued June 19, 1962. As examples of suitable combinations of auxiliary developing agents, mention may be made of l-phenyl-3-pyrazolidone in combination with p-benzylaminophenol and l-phenyl- 3-pyrazolidone in combination with 2,5bisethylenimino-hydroquinone. Such auxiliary developing agents may be employed in the liquid, processing composition or they may be initially incorporated, at least in part, in any one or more of the silver halide emulsion strata, the strata containing the dye developers, the interlayers, the overcoat layer, the image-receiving layer, or in any other auxiliary layer, or layers, of the film unit. It may be noted that at least a portion of the dye developer oxidized during development may be oxidized and immobilized as a result of a reaction, e.g., an energy-transfer reaction, with the oxidation product of an oxidized auxiliary developing agent, the latter developing agent being oxidized by the development of exposure silver halide. Such a reaction of oxidized developing agent with unoxidized dye developer would regenerate the auxiliary developing agent for further reaction with the exposed silver halide.

In addition, development may be effected in the presence of an oniurn compound, particularly a quaternary ammonium compound, in accordance with the processes disclosed in U. S. Pat. No. 3,173,786, issued Mar. 16, 1965.

It will be apparent that the relative proportions of the agents of the diffusion transfer processing composition may be altered to suit the requirements of the operator. Thus, it is within the scope of this invention to modify the herein described developing compositions by the substitution of preservatives, alkalies, etc., other than those specifically mentioned, provided that the pH of the composition is initially at the first pH and solvent concentration required. When desirable, it is also contemplated to include, in the developing composition, components such as restrainers, accelerators, etc. Similarly, the concentration of various components may be varied over a wide range and when desirable adaptable components may be disposed in the photosensitive element, prior to exposure, in a separate permeable layer of the photosensitive element and/or in the photosensitive emulsion.

In all examples of this specification, percentages of components are given by weight unless otherwise indicated.

An extensive compilation of specific dye developers particularly adapted for employment in photographic diffusion transfer processes is set forth in aforementioned U. S. Pat. No. 2,983,606 and in the various copending U. S. applications referred to in that patent, especially in the table of U. S. applications incorporated by reference into the patent as detailed in column 27. As examples of additional U. S. patents detailing specific dye developers for photographic transfer process use, mention may also be made of U. S. Pat. Nos.

3,135,606; 3,135,734; 3,141,772; 3,142,565; and the like.

As additional examples of synthetic, film-forming, permeable polymers particularly adapted to retain dispersed dye developer, mention may be made of nitrocarboxymethyl cellulose, as disclosed in U. S. Pat. No. 2,992,104; an acylamidobenzene sulfo ester of a partial sulfobenzal of polyvinyl alcohol, as disclosed in U. S. Pat. No. 3,043,692; polymers of N-alkyl-afiunsaturated carboxamides and copolymers of N-alkyl-u,B-carboxamides with N-hydroxyalkyl-a, B-unsaturated carboxamides, as disclosed in U. S. Pat. No. 3,069,263; copolymers of vinylphthalimide and a,B-unsaturated carboxylic acids, as disclosed in U. S. Pat. No. 3,061,428; copolymers of N-vinylpyrrolidones and a,B-unsaturated carboxylic acids and terpolymers of N-vinylpyrrolidones, a,B-unsaturated carboxylic acids and alkyl esters of a,B-unsaturated carboxylic acids, as disclosed in U. 5. Pat. No. 3,044,873; copolymers of N,N-dialkyl-a,B-unsaturated carboxamides with a,B-unsaturated carboxylic acids, the corresponding amides of such acids, and copolymers of N-aryl and N-cycloalkyl-a,B-unsaturated carboxamides with a,B-unsaturated carboxylic acids, as disclosed in U. S. Pat. No. 3,069,296; and the like.

In addition to conventional techniques for the direct dispersion of a particulate solid material in a polymeric, or colloidal, matrix such as ball-milling and the like techniques, the preparation of the dye developer dispersion may also be obtained by dissolving the dye in an appropriate solvent, or mixture of solvents, and the resultant solution distributed in the polymeric binder, with optional subsequent removal of the solvent, or solvents, employed, as for example, by vaporization where the selected solvent, or solvents, possesses a sufficiently low boiling point or washing where the selected solvent, or solvents, possesses a sufficiently high differential solubility in the wash medium, for example, water,

when measured against the solubility of the remaining composition components, and/or obtained by dissolving both the polymeric binder and dye in a common solvent.

For further detailed treatment of solvent distribution systems of the types referred to above, and for an extensive compilation of the conventional solvents traditionally employed in the art to effect distribution of photographic color-providing materials in polymeric binders, specifically for the formation component layers of photographic film units, reference may be made to U. S. Pat. Nos. 2,269,158; 2,322,027; 2,304,939; 2,304,940; 2,801,171; and the like.

Although the invention has been discussed in detail throughout employing dye developers, the preferred image-providing materials, it will be readily recognized that other, less preferred, image-providing materials may be substituted in replacement of the preferred dye developers in the practice of the invention. For example, there may be employed dye image-forming materials such as those disclosed in U. S. Pat. Nos. 2,647,049;

2,661,293; 2,698,244; 2,698,798; 2,802,735; 3,148,062; 3,227,550; 3,227,551; 3,227,552; 3,227,554; 3,243,294; 3,330,655; 3,347,671; 3,352,672; 3,364,022; 3,443,939; 3,443,940; 3,443,941; 3,443,943; etc., wherein color diffusion transfer processes are described which employ color coupling techniques comprising, at least in part, reacting one or more color developing agents and one or more color formers or couplers to provide a dye transfer image to a superposed image-receiving layer and those disclosed in U. S. Pat. No. 2,774,668 and 3,087,817, wherein color diffusion transfer processes are described which employ the imagewise differential transfer of complete dyes by the mechanisms therein described to provide a transfer dye image to a continguous image-receiving layer, and thus including the employment of image-providing materials in whole or in part initially insoluble or nondiffusible as disposed in the film unit which diffuse during processing as a direct or indirect function of exposure.

Although the preceding description of the invention has been couched in terms of the preferred photosensitive component construction wherein at least two selectively sensitized photosensitive strata are in contiguous coplanar relationship and, specifically, in terms of the preferred tripack type structure comprising aredsensitive silver halide emulsion stratum, a greensensitive silver halide emulsion stratum and a bluesensitive silver halide emulsion stratum having associated therewith, respectively, a cyan dye developer, a magenta dye developer and a yellow dye developer, the photosensitive component of the film unit may comprise at least two sets of selectively sensitized minute photosensitive elements arranged in the form of a photosensitive screen wherein each of the minute photosensitive elements has associated therewith, for example, an appropriate dye developer in or behind its respective silver halide emulsion portion. In general, a suitable photosensitive screen will comprise minute red-sensitized emulsion elements, minute greensensitized emulsion elements and minute bluesensitized emulsion elements arranged in side-by-side relationship in a-screen pattern and having associated therewith, respectively, a cyan, a magenta and a yellow dye developer.

The present invention also includes the employment of a black dye developer and the use ofa mixture of dye developers adapted to provide a black-and-white transfer image, for example, the employment of dye developers of the three subtractive colors in an appropriate mixture in which the quantities of the dye developers are proportioned such that the colors combine to provide black.

Where in the specification, the expression positive image has been used, this expression should not be interpreted in a restrictive sense since it is used primarily for purposes of illustration, in that it defines the image produced on the image-carrying layer as being reversed, in the positive-negative sense, with respect to the image in the photosensitive emulsion layers. As an example of an alternative meaning for positive image, assume that the photosensitive element is exposed to actinic light through a negative transparency. in this case, the latent image in the photosensitive emulsion layers will be a positive and the dye image produced on the image-carrying layer will be a negative. The expression positive image" is intended to cover such an image produced on the image-carrying layer.

It will be recognized that, by reason of the preferred film units structural parameters, the transfer image formed upon directed exposure of the film unit to a selected subject and processing, will be a geometrically reversed image of the subject. Accordingly, to provide transfer image formation geometrically nonreversed, exposure of such film unit should be accomplished through an image-reversing optical system such a cam era possessing an image-reversing optical system.

In addition to the described essential layers, it will be recognized that the film unit may also contain one or more subcoats or layers, which, in turn, may contain one or more additives such as plasticizers, intermediate essential layers for the purposes, for example, of improving adhesion, and that any one or more of the described layers may comprise a composite of two or more strata of the same, or different, components and which may be contiguous, or separated from, each other, for example, two or more neutralizing layers or the like, one of which may be disposed intermediate the cyan dye image-forming component retaining layer and the dimensionally stable opaque layer.

Since certain changes may be made in the above product and process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a imiting sense.

What is claimed is:

1. A photographic film unit comprising photosensitive silver halide and an initially substantially colorless precursor of an alkyl viologen, wherein said precursor is represented by the formulae:

and

wherein R and R, are alkyl groups and X is an acid anion.

2. A product as defined in claim 1 wherein said film unit comprises a support carrying a photosensitive silver halide layer having associated therewith said pre cursor.

3. A product as defined in claim 2 wherein said precursor is disposed in a layer adjacent to said photosensitive layer.

4. A product as defined in claim 2 wherein said precursor is disposed in said silver halide layer.

5. A product as defined in claim 2 wherein said silver halide layer has additionally associated therewith a photographic silver halide developing agent.

6. A product as defined in claim 5 wherein said photographic silver halide developing agent is a dye.

7. A product as defined in claim 2 which comprises a plurality of layers including a support layer carrying on one surface a photosensitive silver halide emulsion layer having associated therewith an image-forming material which is processing composition soluble and diffusible as a function of the point-to-point degree of silver halide emulsion exposure; an initially substantially colorless precursor of an alkyl viologen; and a layer adapted to receive solubilized image-forming material diffusing thereto.

8. A product as defined in claim 7 which comprises a plurality of layers including an opaque support layer carrying on one surface, in order, a silver halide emulsion layer having associated therewith a dye imageforming material which is processing composition soluble and diffusible as a function of the point-to-point degree of exposure of said silver halide emulsion; an ini tially substantially colorless precursor of an alkyl viologen; reflecting means adapted to mask dye imageforming material associated with said silver halide emulsion layer subsequent to processing of the film unit; and a polymeric layer dyeable by said dye imageforming material.

9. A product as defined in claim 8 which is adapted to be processed by passing said film unit between a pair of juxtaposed pressure-applying members and which comprises, in combination:

a photosensitive element including a composite structure containing, as essential layers, in sequence, a first dimensionally stable layer opaque to incident actinic radiation; a photosensitive silver halide emulsion layer having associated therewith a dye image-forming material which is processing composition soluble and diffusible as a function of exposure of the photosensitive silver halide emulsion layer to actinic radiation; a polymeric layer dyeable by said dye image-forming material; a second dimensionally stable layer transparent to incident actinic radiation; and means securing said layers in substantially fixed relationship;

a rupturable container retaining an alkaline processing composition containing reflecting agent fixedly positioned and extending transverse a leading edge of said photosensitive element to effect unidirectional discharge of said containers processing composition between said dyeable polymeric layer and the photosensitive silver halide emulsion layer next adjacent thereto upon application of compressive force to said container; and

an alkyl viologen dye precursor in a layer intermediate said first dimensionally stable layer opaque to incident actinic radiation and said layer dyeable by said dye image-forming material.

10. A product as defined in claim 9 wherein said refleeting agent is titanium dioxide.

1 I. A product as defined in claim 8 wherein said reflecting means, taken together with the alkaline hydrolysis product of said compound, are adapted to prevent further exposure of selectively photoexposed silver halide emulsion during processing in the presence of radiation actinic thereto and incident on the surface of said film unit opposite said opaque support layer.

13. A product as defined in claim 9 including at least one acid reacting polymeric positioned intermediate at least one of said first dimensionally stable opaque layer and the photosensitive silver halide emulsion layer next adjacent thereto, and said second dimensionally stable transparent layer and the dyeable polymeric layer next adjacent thereto and said processing composition comprises an aqueous alkaline processing solution.

13. A product as defined in claim 12 wherein said polymeric acid layer contains sufficient acidifying function to effect reduction of said processing composition from a first pH at which said dye image-forming material is substantially soluble and diffusible to a second pH at which said image-forming material is substantially non-diffusible.

14. A product as defined in claim 13 wherein said dye image-forming material comprises a dye which is a silver halide developing agent.

15. A product as defined in claim 9 wherein said precursor is:

16. A product as defined in claim 9 wherein said precursor is:

wherein R and R are alkyl groups and X is an acid anion, to provide to said photosensitive layer a latent image as a function of the point'to-point degree of exposure of said photosensitive layer and contacting said photosensitive layer with an aqueous alkaline processing composition which comprises a silver halide developing agent, for a time sufficient to develop said latent image to a visible image.

18. A process as defined in claim 17 including the step of separating said processing composition from contact with said photosensitive element subsequent to substantial visible image formation.

19. A process of forming photographic images as defined in claim 17 wherein said precursor is initially disposed in an aqueous alkaline processing composition permeable layer of said element adjacent said photosensitive layer.

20. A process as defined in claim 17 wherein said compound is dispersed in said photosensitive layer.

21. A process as defined in claim 17 which comprises, in combination, the steps of:

a. exposing a photographic film unit which is adapted to be processed by passing said unit between a pair of juxtaposed pressure-applying members and which includes, in combination, a photosensitive element comprising a composite structure containing, as essential layers, in sequence, a first dimensionally stable layer opaque to incident actinic radiation; a photosensitive silver halide emulsion layer having associated therewith a dye imageforming material which is processing composition soluble and diffusible as a function of exposure of the photosensitive silver halide emulsion layer to actinic radiation; and a compound represented by the formulae:

and

H4 yt wherein R and R each are alkyl groups and X is an acid anion; a polymeric layer dyeable by said dye imageforming material; a second dimensionally stable layer transparent to incident actinic radiation; and means securing said layers in substantially fixed relationship; means for interposing a reflecting agent intermediate said dyeable polymeric layer and said photosensitive silver halide emulsion layer and associated dye imageforming material subsequent to photoexposure of said film unit;

a rupturable container retaining an aqueous alkaline processing composition fixedly positioned and extending transverse a leading edge of said photosensitive element to effect unidirectional discharge of the containers processing composition intermediate said dyeable polymeric layer and the photosensitive silver halide emulsion layer next adjacent thereto upon application of compressive force to said container;

b. applying compressive force to said rupturable container to effect unidirectional discharge of the containers processing composition intermediate said dyeable polymeric layer and said photosensitive silver halide emulsion layer;

6. effecting thereby substantial development of said silver halide emulsion, disposition of said reflecting agent intermediate said dyeable polymeric layer and said photosensitive silver halide emulsion layer generating in an alkyl viologen dye;

d. as a result of said development, forming an imagewise distribution of mobile dye image-forming material, as a function of the point-to-point degree of exposure of said emulsion;

. transferring, by diffusion, at least a portion of said imagewise distribution of mobile dye imageforming material to said dyeable polymeric layer to provide a dye image thereto in terms of said imagewise distribution; and

f. maintaining said composite structure intact subsequent to said processing.

22. A process as defined in claim 21 wherein said alkyl viologen dye is methylviologen. 

2. A product as defined in claim 1 wherein said film unit comprises a support carrying a photosensitive silver halide layer having associated therewith said precursor.
 3. A product as defined in claim 2 wherein said precursor is disposed in a layer adjacent to said photosensitive layer.
 4. A product as defined in claim 2 wherein said precursor is disposed in said silver halide layer.
 5. A product as defined in claim 2 wherein said silver halide layer has additionally associated therewith a photographic silver halide developing agent.
 6. A product as defined in claim 5 wherein said photographic silver halide developing agent is a dye.
 7. A product as defined in claim 2 which comprises a plurality of layers including a support layer carrying on one surface a photosensitive silver halide emulsion layer having associated therewith an image-forming material which is processing composition soluble and diffusible as a function of the point-to-point degree of silver halide emulsion exposure; an initially substantially colorless precursor of an alkyl viologen; and a layer adapted to receive solubilized image-forming material diffusing thereto.
 8. A product as defined in claim 7 which comprises a plurality of layers including an opaque support layer carrying on one surface, in order, a silver halide emulsion layer having associated therewith a dye image-forming material which is processing composition soluble and diffusible as a function of the point-to-point degree of exposure of said silver halide emulsion; an initially substantially colorless precursor of an alkyl viologen; reflecting means adapted to mask dye image-forming material associated with said silver halide emulsion layer subsequent to processing of the film unit; and a polymeric layer dyeable by said dye image-forming material.
 9. A product as defined in claim 8 which is adapted to be processed by passing said film unit between a pair of juxtaposed pressure-applying members and which comprises, in combination: a photosensitive element including a composite structure containing, as essential layers, in sequence, a first dimensionally stable layer opaque to incident actinic radiation; a photosensitive silver halide emulsion layer having associated therewith a dye image-forming material which is processing composition soluble and diffusible as a function of exposure of the photosensitive silver halide emulsion layer to actinic radiation; a polymeric layer dyeable by said dye image-forming material; a second dimensionally stable layer transparent to incident actinic radiation; and means securing said layers in substantially fixed relationship; a rupturable container retaining an alkaline processing composition containing reflecting agent fixedly positioned and extending transverse a leading edge of said photosensitive element to effect unidirectional discharge of said container''s processing composition between said dyeable polymeric layer and the photosensitive silver halide emulsion layer next adjacent thereto upon application of compressive force to said container; and an alkyl viologen dye precursor in a layer intermediate said first dimensionally stable layer opaque to incident actinic radiation and said layer dyeable by said dye image-forming material.
 10. A product as defined in claim 9 wherein said reflecting agent is titanium dioxide.
 11. A product as defined in claim 8 wherein said reflecting means, taken together with the alkaline hydrolysis product of said compound, are adapted to prevent further exposure of selectively photoexposed silver halide emulsion during processing in the presence of radiation actinic thereto and incident on the surface of said film unit opposite said opaque support layer.
 12. A product as defined in claim 9 including at least one acid reacting polymeric positioned intermediate at least onE of said first dimensionally stable opaque layer and the photosensitive silver halide emulsion layer next adjacent thereto, and said second dimensionally stable transparent layer and the dyeable polymeric layer next adjacent thereto and said processing composition comprises an aqueous alkaline processing solution.
 13. A product as defined in claim 12 wherein said polymeric acid layer contains sufficient acidifying function to effect reduction of said processing composition from a first pH at which said dye image-forming material is substantially soluble and diffusible to a second pH at which said image-forming material is substantially non-diffusible.
 14. A product as defined in claim 13 wherein said dye image-forming material comprises a dye which is a silver halide developing agent.
 15. A product as defined in claim 9 wherein said precursor is:
 16. A product as defined in claim 9 wherein said precursor is:
 17. A process of forming photographic images which includes, in combination, the steps of exposing a photosensitive element comprising a plurality of layers including a support carrying on one surface a photosensitive silver halide layer and an initially substantially colorless precursor of an alkyl viologen dye, wherein said precursor is represented by the formulae:
 18. A process as defined in claim 17 including the step of separating said processing composition from contact with said photosensitive element subsequent to substantial visible image formation.
 19. A process of forming photographic images as defined in claim 17 wherein said precursor is initially disposed in an aqueous alkaline processing composition permeable layer of said element adjacent said photosensitive layer.
 20. A process as defined in claim 17 wherein said compound is dispersed in said photosensitive layer.
 21. A process as defined in claim 17 which comprises, in combination, the steps of: a. exposing a photographic film unit which is adapted to be processed by passing said unit between a pair of juxtaposed pressure-applying members and which includes, in combination, a photosensitive element comprising a composite structure containing, as essential layers, in sequence, a first dimensionally stable layer opaque to incident actinic radiation; a photosensitive silver halide emulsion layer having associated therewith a dye image-forming material which is processing composition soluble and diffusible as a function of exposure of the photosensitive silver halide emulsion layer to actinic radiation; and a compound represented by the formulae:
 22. A process as defined in claim 21 wherein said alkyl viologen dye is methylviologen. 